The production of acetic anhydride, by the ketene process, is well known. The method comprises: the thermal decomposition of acetic acid at high temperatures utilizing, for example, a triethyl phosphate dehydration catalyst to produce ketene (I), which is subsequently reacted with excess acetic acid to obtain acetic anhydride (II):

The first step of the process is conducted at low pressure and elevated temperature, typically in excess of 700° C. Catalyst in the product stream may be neutralized with ammonia. The process is widely employed; however, it is capital intensive especially because water generated in step I needs to be removed and acetic acid needs to be removed and recovered. In other words, weak acid recovery adds significantly to the required capital and also impacts operating energy costs adversely. Representative references relating to various aspects of acetic anhydride and ketene production are discussed briefly below.
U.S. Pat. No. 4,455,439 to Hoechst AG, Jun. 19, 1984, describes a process for the preparation of ketene by the thermal, catalytic cracking of acetic acid under reduced pressure. The hot cracked gasses are then cooled to 0° to −10° C. and water, unreacted acetic acid, and acetic anhydride are condensed.
U.S. Pat. No. 4,737,318 to Daicel Chemical Industries, Apr. 12, 1988, describes a process for recovering acetic anhydride from an aqueous solution containing acetic anhydride and acetic acid, which comprises a condensate obtained in a step of cooling a decomposition gas formed in the production of ketene by pyrolyzing acetic acid and cooling the formed gas.
A continuous process for refining acetic anhydride produced by the reaction of ketene and acetic acid is described in U.S. Pat. No. 5,264,087 to Eastman Kodak, Nov. 23, 1993. The process involves a vacuum distillation step, which results in the production of high purity acetic anhydride.
U.S. Patent Application No. 2001/0029309 to Nishioka et al. describes a further purification step in which distilled acetic anhydride is treated with ozone to reduce the diketene content.
Another method for reducing diketene in purified acetic anhydride, described in Japanese Patent No. 41021981 to Nihon Gosei Company, consists of heating the reaction liquid in the presence of diketene polymerization catalysts such as an alkali metal hydroxide alcoholate, sodium acetate, or organic bases.
The production of alkyl esters of acetic acid, from various alkanols, is also well known. Here again, water removal is a significant component of capital and operating expense. Some representative patents are discussed immediately below.
U.S. Pat. No. 4,481,146 to Hoechst AG, Nov. 6, 1984, describes a process for the preparation of an ethyl ester from ethanol-containing mixtures of aliphatic alcohols, which comprises esterifying the alcohols with a carboxylic acid in the presence of an acid catalyst in a distilling column and separating in the same column the ethyl ester continuously from the ester mixture obtained.
A method for making esters of acetic acid, which is a catalytic distillation process utilizing solid acidic catalysts for the esterification of acetic acid with alcohols is described in U.S. Pat. No. 5,998,658 to Industrial Technology Research Institute, Dec. 7, 1999.
U.S. Pat. No. 6,028,215 to BASF AG, Feb. 22, 2000, describes a process for preparing esters from alcohol and carboxylic acid by feeding a mixture of alcohol and carboxylic acid into a distillation column with separated sections containing reactive and conventional internals, reaction of the alcohol and the carboxylic acid in the reactive internals in the presence of a heterogeneous catalyst, distillative separation of the evolving reaction mixture into the higher boiling ester and a lower boiling azeotrope containing alcohol, water and ester, and separation of the azeotrope in a phase separator.
U.S. Pat. No. 6,458,992 to Sulzer Chemtech AG, Oct. 1, 2002, relates to a process for the synthesis of butyl acetate by esterification of acetic acid with butanol by combined distillation and chemical reaction utilizing a column in which separation of the reaction products takes place together with the esterification in catalytically active separation equipment.
U.S. Pat. No. 6,693,213 to Sulzer Chemtech AG, Feb. 17, 2004, describes a method of ethyl acetate synthesis by esterification of acetic acid with ethyl alcohol or by reaction of acetic anhydride with ethyl alcohol, which uses catalytic distillation in a column, during which a reaction on a catalytically active filling and a rectification and separation of reaction products take place simultaneously.
In any event, there is a need in the art to reduce capital required for purification and to increase yields as well as operating efficiency. The present invention meets these needs by concurrently producing acetic anhydride and acetate esters utilizing integrated production equipment.